Recently, investigation and development on various display elements have been actively made. Among others, organic electroluminescent (EL) elements are being watched as promising display elements since they can emit high-luminance luminescence at a low driving voltage. For instance, an organic EL element having a thin layer formed by vapor deposition of an organic compound is known as described in Applied Physics Letters, Vol. 51, page 913 (1987). The organic EL element described therein has a laminated layer structure of an electron-transporting material and a hole-transporting material, and its luminescent characteristics are greatly improved in comparison with conventional EL elements of single layer type.
In order to improve luminescent efficiency of the EL element of laminated type described above, a method of doping a fluorescent dye is known. For example, an organic EL element doped with a coumarin dye described in Journal of Applied Physics, Vol. 65, page 3610 (1989) exhibits remarkably improved luminescent efficiency as compared with an organic EL element without doping (non-doped type element). However, the doped element is inferior in production aptitude, for example, because it is necessary to control the dope amount subtly. Accordingly, it was desired to develop a non-doped type element that emits highly efficiently.
In the field of organic EL elements, color of luminescence requested may be varied and it is possible to obtain light having the desired wavelength by changing the kind of fluorescent dye to be employed.
However, only a small number of fluorescent dyes emitting blue to blue-green light which emits highly efficiently light having the desired wavelength and have good durability are known, and a further development has been desired.